Genetics Northern California

Duchenne Muscular Dystrophy

What is Duchenne muscular dystrophy (DMD)?
How common is Duchenne muscular dystrophy?
What causes Duchenne muscular dystrophy?
How is Duchenne muscular dystrophy diagnosed?
How is Duchenne muscular dystrophy treated?
Where can I get more information about Duchenne muscular dystrophy?

What is Duchenne muscular dystrophy?
Duchenne muscular dystrophy (DMD) is a genetic disorder that causes weak muscles and muscle wasting (muscle loss). DMD affects the muscles that move the body, as well as the muscles in the heart and diaphragm (the main muscle for breathing). The muscle weakness gets worse as a person grows older. The condition mostly affects boys, but in rare cases, it can affect girls.

Boys with DMD are slow to start walking and have more trouble with physical activities (e.g., running, jumping, climbing stairs, throwing a ball). As the muscles in the legs weaken, a wheelchair is eventually needed. Boys with DMD may start using a wheelchair around 12 years old, but the exact age is not predictable. Over time, the heart and the breathing muscles also become weaker. The most common cause of death is related to difficulty breathing (pulmonary involvement) or breakdown of the heart muscle. Improved treatments are leading to longer survival; however, life expectancy is still shortened for a person with DMD. 

Learning in DMD - Boys with DMD usually have IQ scores that fall in the normal range, but learning difficulties may be present. Areas of learning that include memory and executive function (the ability to plan and organize) are most likely to be affected. 

Females can be silent carriers of DMD and may show no signs or have minor muscle weakness. Very few women have serious medical problems related to DMD.

How common is Duchenne muscular dystrophy?
About 1 in every 3500 boys is born with DMD worldwide.

What causes Duchenne muscular dystrophy?
Duchenne muscular dystrophy is caused by a mutation (genetic change) in a gene called DMD. This gene makes a protein called dystrophin, which is needed to keep muscles healthy.  A person with DMD is completely (or almost completely) missing the dystrophin protein. Without this protein, the muscles slowly break down. Mutations in the dystrophin gene can also cause a related condition called Becker muscular dystrophy (BMD). A person with BMD makes more dystrophin than someone with DMD, so muscle problems start later in life and are less predictable.

Duchenne muscular dystrophy is an X-linked condition. That means the gene is located on the X-chromosome. Boys have one X chromosome inherited from their mother and one Y chromosome from their father. DMD is often inherited from a mother who is a silent carrier for the condition. However, about 1 in every 3 cases of DMD is not inherited. DMD sometimes happens due to a new genetic change (de novo mutation) when an egg is formed.

How is Duchenne muscular dystrophy diagnosed?
Duchenne muscular dystrophy is suspected based on clinical features. There are often differences in how a boy with DMD walks or runs, how he goes up and down stairs, how he stands up when sitting on the ground, and the way his leg muscles appear. The diagnosis is confirmed by measuring a protein called creatine kinase (CK) in a blood sample. CK levels show how fast the muscles are breaking down. In boys with DMD, the amount of CK is generally 10 times higher than normal. A sample of the muscles (muscle biopsy) was once used to help confirm the diagnosis. Since genetic testing became available, a muscle biopsy is rarely necessary. A family history of DMD can be helpful in making an early diagnosis. In the future, it may be possible to screen newborn boys for DMD.

Genetic Testing - Genetic testing may be done to confirm a diagnosis or to identify the specific mutation in a family. Nearly all males with DMD have a mutation in the dystrophin gene that can be found by genetic testing. When a mutation has been found in someone with DMD, carrier testing can be offered to females in the family and prenatal diagnostic testing is available for future pregnancies.

How is Duchenne muscular dystrophy treated?
There is currently no cure for DMD, but medical treatment may help slow the progression of the disease. Steroid therapy can help maintain muscle strength and may prolong the ability to walk. In addition, all boys with DMD should be monitored by a cardiologist (heart specialist). The cardiologist may use medications to manage heart symptoms. Female carriers of DMD should also have a heart evaluation. A special education evaluation may be requested when there are concerns about learning or development. Breathing support may be needed at older ages.

Researchers are actively looking for more effective treatments. To learn more about research opportunities contact one of the support organizations below or go to Clinicaltrials.gov.

Where can I get more information about Duchenne muscular dystrophy?
NIH: Genetics Home Reference on Duchenne and Becker Muscular Dystrophy - General information about DMD and BMD provided as a service of the U.S. National Library of Health. Links to many related sites are included on the page.
GeneReviews: Dystrophinopathies – Detailed information about DMD and BMD intended for medical professionals. 

Family Support Resources
Muscular Dystrophy Association- Duchenne Muscular Dystrophy Page: https://www.mda.org/disease/duchenne-muscular-dystrophy
Parent Project Muscular Dystrophy: http://www.parentprojectmd.org/

Last reviewed: January 26, 2018
Reviewed by: Kimberly Barr, MS, LCGC